1. Field of the Invention
The present invention relates to a shape analysis method and a shape analysis program. Concretely, the invention relates to the shape analysis method for analyzing shape measured data obtained by measuring a contour shape of a workpiece to be measured and calculating or evaluating geometric properties such as roundness, a center position or dimensions of the contour shape. More particularly, the invention relates to the art of specifying an evaluation range in the case of analyzing a shape.
2. Description of the Related Art
Various shape measuring apparatuses for measuring a contour shape of a workpiece to be measured are known. Contour shape data of the workpiece to be measured is obtained by extracting a contour from image data imaged or scanning a surface of the workpiece to be measured by, for example, a contact probe or a non-contact probe. In addition, the shape measuring apparatuses have various names or kinds such as a three-dimensional coordinate measuring machine, a roundness measuring machine or a surface roughness measuring machine, but any devices capable of measuring the contour shape of the workpiece to be measured even when names or applications differ are included in the shape measuring apparatuses.
It may become necessary to analyze measured data obtained by measurement by the shape measuring apparatus and evaluate working accuracy of the workpiece to be measured. For example, it becomes necessary to evaluate straightness, curvature, a center position of a circle of curvature, dimensions, etc. in a certain range in the measured data. Hence, the shape measuring apparatus may have functions of applying a geometric element to a certain range in measured data or calculating straightness, curvature, a center position of a circle of curvature, dimensions, etc. of the measured data based on the applied geometric element (for example, JP-A-2006-214870, JP-A-2008-116392 and JP-A-11-118444).
Here, the geometric element refers to a geometric shape such as a straight line, a circular arc, a circle or a rectangle. In the present specification, application of the geometric element to measured data in a certain range or calculation of a size, a shape, a position, etc. of the geometric element may be represented as “calculation of geometric properties”. Further, in addition to primary geometric properties of directly calculating an individual geometric element, secondary geometric properties may be computed by further computation from numerical values indicating these primary geometric properties. Examples of the secondary geometric properties include, for example, coordinates of a point of intersection between one straight line and another straight line, or a distance between a center point of one circular arc and a center point of another circular arc.
In the present specification, a computation program for calculating geometric properties based on measured data may be called a “PART program”.
Now, it is necessary to specify, for example, a kind of geometric element or a range of data targeted for computation in the case of evaluating accuracy of work from the measured data. Conventionally, a user has inputted specification of the kind of geometric element or the range sequentially manually.
A Conventional procedure will be described briefly.
It is assumed that the target work has a shape as shown in FIG. 35. When this work is measured, as shown in FIG. 36, an upper surface will obtain a data string having a horizontal linear line portion L1 from the left end, a downwardly convex circular arc portion C1 continuous with the line portion L1 and further a linear line portion L2 continuous with the circular arc portion C1.
The data string is displayed on a display screen as shown in FIG. 36. Then, it is herein evaluated whether the circular arc portion C1 is worked so as to have curvature or a center point as designed.
First, a range targeted for evaluation must be specified.
In the case of specifying a range of an x-axis direction, two cursors 21, 22 in a longitudinal direction (z direction) are moved and a range sandwiched between the two cursors 21, 22 is specified as the x-direction range as shown in FIG. 37. In the case of setting a range of a z-axis direction, two cursors 23, 24 in a transverse direction (x direction) are moved and a range sandwiched between the two cursors 23, 24 is specified as the z-direction range as shown in FIG. 38. Then, a data string in a rectangular range set thus is specified as a geometric element so as to apply a “circle”. Then, the PART program performs computation in which a circular shape is applied to the data string in the range specified. Accordingly, a radius r of a perfect circle including the circular arc C1, coordinates of a center point O, a deviation from a perfect circle, etc. are calculated as shown in FIG. 39. Such geometric properties are calculated with respect to the line portion L1, the line portion L2, etc. in addition to the circular arc portion C1. In this manner, a shape of the measured data is evaluated.
In the case of evaluating the shape, an evaluation range must be specified as described above, but in this case, the x range and the z range must be specified and operation of plural inputs is required. Such input operation is very complicated and has a problem of requiring time and effort. Inexperience takes considerable time and further, plural evaluation targets require substantial time.
Also, when a user specifies an evaluation range manually each time, the evaluation range differs every user, and even for the same user, the evaluation range differs at different times.
For example, when a relatively narrow range is specified as shown in a range S1 of FIG. 40, evaluation of roundness can be increased. In the case of having a potential intention to want to increase the evaluation, a narrow range may be specified even in an unintentional case. However, of course, in the case of making rigorous and correct evaluation, a properly sufficiently wide range should be specified as shown in a range S2. On the other hand, the edge portion naturally has deformation such as shear drops or burrs, so that when too wide a range S3 is specified, there is fear that a circular arc cannot be applied well. Thus, an evaluation result may greatly differ depending on only a small difference in specification of the evaluation range.